This invention relates to a process for the treatment or removal of impurities such as arsenic, antimony and bismuth, such as, for example, generated as by-products during smelting and refining of copper concentrates or when present in an ore or concentrate being treated by a hydrometallurgical metal extraction process. It also relates to the treatment of other impurities, such as fluoride and mercury.
Arsenic, antimony and bismuth are often found in naturally occurring copper (sulphide) ores, and therefore each or several of them are often a minor constituent of copper concentrates which are obtained from sulphide ore by means of the well-established floatation processes.
These elements have little or no commercial value in copper concentrates, unlike other base metals which may also occur in copper concentrates, such as zinc, nickel or cobalt, but instead constitute deleterious impurities which must be removed during the subsequent refining process on the concentrate, otherwise the product of such refining process, i.e. copper metal, will be impure and lose value.
If copper concentrates containing such deleterious impurities are processed by the conventional smelting and refining processes, the impurities are commonly separated out at different stages of the process into a variety of by-products.
The by-products may be solids, such as fine dusts collected from the smelter, or liquids, such as purge streams, derived from the gas cleaning section of an acid plant attached to the smelter.
These by-products, due to their hazardous or toxic nature, are often difficult and expensive to dispose of. In addition, these materials are regulated and usually cannot be disposed of in a general tailings area where the tailings from the concentration process are frequently sent. As a result, concentrates containing the impurities are often too expensive to process and the metal values cannot be recovered economically.
Another impurity which sometimes occurs in copper sulphide ores is fluorine. It can generally be separated out at the concentration stage fairly efficiently, by rejecting the fluoride-containing minerals to the tailings stream, but in some circumstances concentrates do contain significant amounts of fluorine. This causes difficulty for the smelting and refining process, and therefore there is a maximum allowed level of fluorine in concentrates, above which it is a penalty element, and above a certain higher level may even preclude the sale of the concentrate.
According to the invention there is provided a method of treating a by-product from a copper smelting or refining process, which by-product contains an element selected from the group consisting of As, Sb, Bi and Hg, comprising the steps of: subjecting a copper ore or concentrate also containing iron and a source of bisulphate or sulphate ions to pressure oxidation at an elevated temperature and pressure in the presence of oxygen and an acidic solution containing halide ions; and subjecting said by-product to the pressure oxidation together with said ore or concentrate to obtain a resulting pressure oxidation slurry containing copper and a compound of said element.
Also according to the invention there is provided a method of treating a copper ore or concentrate also containing fluoride comprising the steps of subjecting the ore or concentrate along with a source of bisulphate or sulphate ions to pressure oxidation at an elevated temperature and pressure in the presence of oxygen and an acidic solution containing halide ions, the halide ions being selected from the group consisting of chloride ions and bromide ions, to obtain a resulting pressure oxidation slurry; subjecting the slurry to a liquid/solid separation step to obtain a resulting pressure oxidation filtrate and a solid residue; and continuously recycling the pressure oxidation filtrate to the pressure oxidation thereby to solubilize the fluoride up to a saturation concentration in the pressure oxidation filtrate, to establish an equilibrium condition whereby no further nett dissolution of fluoride takes place and substantially all fluoride in the ore or concentrate goes into the solid residue.
Further according to the invention there is provided a method of dispensing with an impurity contained in a copper ore or concentrate, which impurity is in the form of an element selected from the group consisting of As, Sb, Bi and Hg, comprising the steps of subjecting a copper ore or concentrate also containing iron and a source of bisulphate or sulphate ions to pressure; oxidation at an elevated temperature and pressure in the presence of oxygen and an acidic solution containing halide ions; and subjecting said by-product to the pressure oxidation together with said ore or concentrate to obtain a resulting pressure oxidation slurry containing copper and a compound of said element.
Further objects and advantages of the invention will become apparent from the description of preferred embodiments of the invention below.